Imaging lateral heterogeneity in the northern Apennines from time reversal of reflected surface waves
Imaging lateral heterogeneity in the northern Apennines from time reversal of reflected surface waves
复制标题
从反射表面波的时间反演对亚平宁山脉北部的横向异质性进行成像
DOI：
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发表时间：
2007
期刊：
影响因子：
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通讯作者：
J. Tromp
中科院分区：
文献类型：
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作者：
D. Stich;P. Danecek;A. Morelli;J. Tromp
概要：来自更广阔的阿尔卑斯地区的地震图尾波中的显著波至，可能与亚平宁山脉（意大利）北方的Love波的侧向反射有关，在那里，结构的不均匀性导致相速度的突然对比。我们讨论了一种方法，图像的横向不均匀性从反射表面波使用中期，三分量尾波波形作为源的伴随波场，传播的反射时间向后。我们数值计算的尾波波形P速度，S速度和密度的依赖性的三维灵敏度内核，根据伴随和规则的前向波场之间的相关性。我们认为合成尾波波形的一个简化模型的北方亚平宁山脉，以及真实的尾波观测5个中等规模的地震（MW 4.6-5.6）在阿尔卑斯山南部。波的传播是用谱元法模拟的，在真实的数据的情况下，使用三维区域地球模型。单个和组合事件灵敏度内核提供清晰的图像的反射率与北方亚平宁山脉的密度和S波速度的内核。核函数显示，面波反射发生在山脉轴向带附近。除了亚平宁山脉，该方法还能够从尾波波形中成像其他较小的反射率斑块，如阿尔卑斯山南部的伊夫雷亚区。我们的尾波失配内核可以集成在一个基于梯度的波形断层扫描，在那里他们可以提高模型的横向不连续的锐度。
SUMMARY Prominent arrivals in the coda of seismograms from the wider Alpine area can be associated with lateral reflections of Love waves at the northern Apennines mountain chain (Italy), where structural heterogeneity causes an abrupt contrast in phase velocity. We discuss an approach to image lateral heterogeneity from reflected surface waves using intermediate-period, threecomponent coda waveforms as sources for an adjoint wavefield that propagates the reflections backward in time. We numerically compute three-dimensional sensitivity kernels for the dependence of coda waveforms on P velocity, S velocity and density, based upon correlations between the adjoint and the regular forward wavefields. We consider synthetic coda waveforms for a simplified model of the northern Apennines, as well as real coda observations from five moderate magnitude earthquakes (M W 4.6–5.6) in the southern Alps. Wave propagation is simulated using the spectral-element method, for which a 3-D regional earth model is used in the case of real data. Single and combined event sensitivity kernels provide clear images of the reflectivity associated with the northern Apennines in kernels for density and S-wave speed. The kernels show that surface wave reflections occur near the axial zone of the mountain chain. Apart from the Apennines, the approach is able to image other smaller reflectivity patches from the coda waveforms, like the Ivrea zone in the southern Alps. Our coda misfit kernels can be integrated in a gradient-based waveform tomography, where they could enhance the sharpness of the model at lateral discontinuities.